Emission Testing of N ₂ O (Bag Sampling) from Diverse Vehicles by Laser Spectroscopic Motor Exhaust Gas Analyzer 2011-01-1155

The United States Environmental Protection Agency (EPA) has finalized a reporting rule for the Greenhouse Gases (GHGs) emissions including Nitrous Oxide (N₂O) from all sectors of the economy. In addition, EPA and the National Highway Traffic Safety Administration (NHTSA) have been working together on developing a National Program of harmonized regulations to reduce GHGs emissions and improve fuel economy of light-duty vehicles (LDV). As a consequence, the limiting value for N₂O emission from LDV is set to 0.01 g/mile. Considering this regulatory limit of N₂O emission from LDV, if the exhaust gas is diluted and stored in a sample storage bag, the concentration of N₂O becomes very low which requires a highly sensitive analyzer for accurate measurement.

In the previous study, an instrument based on Quantum Cascade Mid-IR Laser (QCL-Mid IR) Spectroscopy has been developed for measuring ultra-low level of N₂O in automobile exhaust gas sampled in a sample storage bag. In this study, the instrument has been used for measuring total and modal mass emissions of N₂O from four different LDVs, all meeting regional emission standards applicable for respective model years. The vehicles included a direct injection (DI) gasoline vehicle, a direct injection diesel vehicle, and two conventional port injection (PI) gasoline vehicles. The main objective is to examine the measurement capability of the instrument and to develop a better understanding of N₂O emissions from diverse catalyst-equipped vehicles. Measurements are conducted on a chassis dynamometer under FTP75 driving cycle both at cold and hot start conditions. Samples are stored in sample storage bags for measurement after being diluted in a Constant Volume Sampling (CVS) system.

It is found from the investigation that the DI gasoline vehicle emits higher N₂O (approximately double) than conventional PI gasoline vehicles. N₂O emission is found to be increased during nitrogen oxides (NO_x) conversion in the catalytic converter. The concentration of N₂O in the sample storage bag becomes very low upon dilution. The laser-based motor exhaust gas analyzer showed strong potential for measuring this ultra-low concentration of N₂O in sample storage bag.